The unbonded coating of metallic substrates with molten plasticized thermoplastic resin has been achieved by a variety of methods. One such method involves the extrusion of vinyl halide resin compositions onto a core or substrate of galvanized steel to secure a coating providing an assured resistance to weather and aging, including oxidizing agents and corrosive constituents of many environments in which this resulting coated product may, in the ordinary course of outdoor usage, be exposed. Coated metallic substrates so secured, have been known, when incorporating suitable plasticizers, to manifest a flexibility without cracking, impact hardness and resistance to abrasion which makes them particularly useful in application to wire to be formed into, for example, chain-link fence. These fence materials present, in addition, an esthetically pleasing appearance.
The metallic substrate of these coated materials is rendered vulnerable, however, where only a single ply of unbonded plastic is present because of the relative ease with which the plastic can be cut and removed in relatively substantial lengths by the deliberate effort of vandals or others, a condition which tends to be prevalent in heavily industrial locations, public playgrounds and the like.
The bonding of a thermoplastic resin coating to the metallic substrate has been known to reduce this ease of removal. This has been accomplished by treating wire, for example, with a primer heated to an elevated temperature and the composite of wire and primer passed through a fluidized bed of vinyl resin powder. The wire substrate used commercially in the practice of this latter process has been found to be ungalvanized steel. Inherent in this process, additionally, has been the formation of a microporous coating of limited thickness, i.e. about 7-10 mils, and this vinyl coating has been found to evidence reduced resistance to ultra-violet radiation over a sustained period. The relative thinness of the coating which can be achieved by this method has been found to permit corrosive atmospheres even in the absence of removal of the coating. This vulnerability is, of course, of particular significance where the substrate is, illustratively, ungalvanized steel. The production of vinyl coated metallic substrates employing plastisols or organosols of vinyl chloride resins has also been projected, but the combination of steps including particularly the removal of diluents from the coating and the absorption of plasticizers in the fusion phase tend to render the processes uneconomic, both by reason of the reduced speeds at which, for example, wire must pass through the coating step, e.g. up to about 300 feet per minute, and the high temperature baking ovens necessary for fusion, utilizing high levels of electric energy.